PROJECT SUMMARY Musculoskeletal (MSK) pain affects 18-32% of youth and places a high level of burden on children, families, and the health care system. During childhood, prevalence of MSK pain increases with age, placing adolescents at highest risk. When MSK pain becomes chronic, youth experience significant psychosocial difficulties, physical disability, and impaired school functioning. Treatment costs of pediatric chronic pain are estimated at $19 billion annually in the United States. There is an urgent need to reduce the costs and impact of pediatric chronic MSK pain, particularly given that risk for pain, disability, and high health care use can extend from adolescence into adulthood. A key first step is identifying mechanisms underlying the transition from acute to chronic MSK pain in youth. A pivotal mechanism thought to underlie chronic pain is sensitization of central pain pathways and impairment in conditioned pain modulation. Research shows differences in pain modulation in children and adults with chronic pain compared to healthy samples, and that poor pain inhibition predictsrisk for future chronic painin adults. A critical gap in knowledge is how pain modulation, psychosocial factors and behavioral vulnerabilities confer risk for the transition from acute to chronic MSK pain in youth. As outlined in the NIH's Federal Pain Strategy Research Report, evaluating episode prospective individuals the course of pain from an acute to a chronic pain state is a top research priority. need for studies examining the transition from acute to chronic pain to identify transition mechanisms and at greatest risk. Further, the report highlights the urgent To fill these important knowledge gaps, we propose the first large-scale longitudinal cohort study of youth with acute MSK pain (n=300) to test a biopsychosocial model of risk for transition from acute to chronic pain. Youth will complete assessments at 4 data waves over one year and using a combination of: a) quantitative sensory testing of the pain modulation b) psychosocial assessment, and c) actigraphic monitoring of sleep, the central aim is to identify mechanisms in the transition from acute to chronic MSK pain. We will also characterize the contribution of sleep deficiencies, cognitive-affective vulnerabilities, parent pain-specific responses, and key child demographic characteristics in conferring risk for poor pain outcomes. The aims of this innovative study address a major gap in current pediatric MSK pain research by informing our understanding of how pain transitions from an acute to chronic state and will provide knowledge of early risk factors for developing chronic MSK pain. Data generated from this proposal will also directly inform our team's development of screening protocols and targeted preventive interventions directed at youth at greatest risk for developing chronic MSK pain. Aligning with the goals of the Federal Pain Strategy Research Report, with this research we shift the focus from treatment of chronic pain to prevention through early identification of at-risk youth.